diff --git a/packages/cli/src/acp-integration/session/Session.test.ts b/packages/cli/src/acp-integration/session/Session.test.ts
new file mode 100644
index 000000000..af98fe25c
--- /dev/null
+++ b/packages/cli/src/acp-integration/session/Session.test.ts
@@ -0,0 +1,174 @@
+/**
+ * @license
+ * Copyright 2025 Qwen
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { Session } from './Session.js';
+import type { Config, GeminiChat } from '@qwen-code/qwen-code-core';
+import { ApprovalMode } from '@qwen-code/qwen-code-core';
+import type * as acp from '../acp.js';
+import type { LoadedSettings } from '../../config/settings.js';
+import * as nonInteractiveCliCommands from '../../nonInteractiveCliCommands.js';
+
+vi.mock('../../nonInteractiveCliCommands.js', () => ({
+  getAvailableCommands: vi.fn(),
+  handleSlashCommand: vi.fn(),
+}));
+
+describe('Session', () => {
+  let mockChat: GeminiChat;
+  let mockConfig: Config;
+  let mockClient: acp.Client;
+  let mockSettings: LoadedSettings;
+  let session: Session;
+  let currentModel: string;
+  let setModelSpy: ReturnType<typeof vi.fn>;
+  let getAvailableCommandsSpy: ReturnType<typeof vi.fn>;
+
+  beforeEach(() => {
+    currentModel = 'qwen3-code-plus';
+    setModelSpy = vi.fn().mockImplementation(async (modelId: string) => {
+      currentModel = modelId;
+    });
+
+    mockChat = {
+      sendMessageStream: vi.fn(),
+      addHistory: vi.fn(),
+    } as unknown as GeminiChat;
+
+    mockConfig = {
+      setApprovalMode: vi.fn(),
+      setModel: setModelSpy,
+      getModel: vi.fn().mockImplementation(() => currentModel),
+    } as unknown as Config;
+
+    mockClient = {
+      sessionUpdate: vi.fn().mockResolvedValue(undefined),
+      requestPermission: vi.fn().mockResolvedValue({
+        outcome: { outcome: 'selected', optionId: 'proceed_once' },
+      }),
+      sendCustomNotification: vi.fn().mockResolvedValue(undefined),
+    } as unknown as acp.Client;
+
+    mockSettings = {
+      merged: {},
+    } as LoadedSettings;
+
+    getAvailableCommandsSpy = vi.mocked(nonInteractiveCliCommands)
+      .getAvailableCommands as unknown as ReturnType<typeof vi.fn>;
+    getAvailableCommandsSpy.mockResolvedValue([]);
+
+    session = new Session(
+      'test-session-id',
+      mockChat,
+      mockConfig,
+      mockClient,
+      mockSettings,
+    );
+  });
+
+  describe('setMode', () => {
+    it.each([
+      ['plan', ApprovalMode.PLAN],
+      ['default', ApprovalMode.DEFAULT],
+      ['auto-edit', ApprovalMode.AUTO_EDIT],
+      ['yolo', ApprovalMode.YOLO],
+    ] as const)('maps %s mode', async (modeId, expected) => {
+      const result = await session.setMode({
+        sessionId: 'test-session-id',
+        modeId,
+      });
+
+      expect(mockConfig.setApprovalMode).toHaveBeenCalledWith(expected);
+      expect(result).toEqual({ modeId });
+    });
+  });
+
+  describe('setModel', () => {
+    it('sets model via config and returns current model', async () => {
+      const result = await session.setModel({
+        sessionId: 'test-session-id',
+        modelId: '  qwen3-coder-plus  ',
+      });
+
+      expect(mockConfig.setModel).toHaveBeenCalledWith('qwen3-coder-plus', {
+        reason: 'user_request_acp',
+        context: 'session/set_model',
+      });
+      expect(mockConfig.getModel).toHaveBeenCalled();
+      expect(result).toEqual({ modelId: 'qwen3-coder-plus' });
+    });
+
+    it('rejects empty/whitespace model IDs', async () => {
+      await expect(
+        session.setModel({
+          sessionId: 'test-session-id',
+          modelId: '   ',
+        }),
+      ).rejects.toThrow('Invalid params');
+
+      expect(mockConfig.setModel).not.toHaveBeenCalled();
+    });
+
+    it('propagates errors from config.setModel', async () => {
+      const configError = new Error('Invalid model');
+      setModelSpy.mockRejectedValueOnce(configError);
+
+      await expect(
+        session.setModel({
+          sessionId: 'test-session-id',
+          modelId: 'invalid-model',
+        }),
+      ).rejects.toThrow('Invalid model');
+    });
+  });
+
+  describe('sendAvailableCommandsUpdate', () => {
+    it('sends available_commands_update from getAvailableCommands()', async () => {
+      getAvailableCommandsSpy.mockResolvedValueOnce([
+        {
+          name: 'init',
+          description: 'Initialize project context',
+        },
+      ]);
+
+      await session.sendAvailableCommandsUpdate();
+
+      expect(getAvailableCommandsSpy).toHaveBeenCalledWith(
+        mockConfig,
+        expect.any(AbortSignal),
+      );
+      expect(mockClient.sessionUpdate).toHaveBeenCalledWith({
+        sessionId: 'test-session-id',
+        update: {
+          sessionUpdate: 'available_commands_update',
+          availableCommands: [
+            {
+              name: 'init',
+              description: 'Initialize project context',
+              input: null,
+            },
+          ],
+        },
+      });
+    });
+
+    it('swallows errors and does not throw', async () => {
+      const consoleErrorSpy = vi
+        .spyOn(console, 'error')
+        .mockImplementation(() => undefined);
+      getAvailableCommandsSpy.mockRejectedValueOnce(
+        new Error('Command discovery failed'),
+      );
+
+      await expect(
+        session.sendAvailableCommandsUpdate(),
+      ).resolves.toBeUndefined();
+      expect(mockClient.sessionUpdate).not.toHaveBeenCalled();
+      expect(consoleErrorSpy).toHaveBeenCalled();
+      consoleErrorSpy.mockRestore();
+    });
+  });
+});